1. Field of the Invention
The present invention relates to glass substrates for flat panel displays and methods for manufacturing the glass substrates.
2. Related Background Art
Flat panel displays with small thickness and low power consumption, such as a thin film transistor (TFT) liquid crystal display and an organic electroluminescence (EL) display, have in recent years been employed as displays for mobile devices and the like. These displays typically include a glass substrate.
There are the following types of TFTs: an amorphous silicon (α-Si) TFT; and a polysilicon (p-Si) TFT. The p-Si TFT is advantageous over the α-Si TFT in terms of screen resolution, display durability, display thickness and weight, and power consumption, and the like, i.e., the p-Si TFT can provide a beautiful screen with a higher resolution, a display with a higher durability, a display with a smaller thickness and a lower weight, and lower power consumption. Conventionally, however, a high temperature treatment is required in production of the p-Si TFT. Therefore, the glass substrate undergoes heat shrinkage and heat shock during production of the p-Si TFT, and therefore, glass other than silica glass cannot be employed. As a result, it is difficult to apply the p-Si TFT to a liquid crystal display.
However, the low-temperature polysilicon (LTPS) TFT, for which the heat treatment is performed at lower temperature, has in recent years been developed, and therefore, the p-Si TFT has been applicable to the flat panel display. As a result, the display of a small device (e.g., a mobile device, etc.) can have a beautiful screen with a high resolution.
Note that the heat treatment in production of the p-Si TFT still requires a temperature of as high as 400 to 600° C. Most of the conventional glass substrates for displays do not have a sufficiently high strain point, and therefore, are likely to undergo significant heat shrinkage due to the heat treatment in production of the p-Si TFT, leading to a non-uniform pixel pitch. Moreover, in recent years, there has been a demand for higher and higher resolutions. Therefore, in order to reduce such a non-uniform pixel pitch, it is highly desirable to reduce the heat shrinkage of the glass substrate during production of the display. Conventionally, glass substrates for displays which have been developed in view of the heat shrinkage problem have been reported (JP 2002-3240A, JP 2004-315354A, and JP 2007-302550A).